The present invention relates to communication loops and more particularly to the isolation of remote sections thereof to facilitate testing or enable correction of faults.
In wire communication systems involving subscriber equipment such as telephones or the like joined at the far end to wire loops that establish connection with a central office, it is often necessary to test the loops for faults. In order to confine test signals to the loop while eliminating interference from the subscriber equipment, it is necessary to disconnect the far end equipment from the loop, and such disconnection should be obtainable under remote control. Disconnection during testing is particularly important where privately owned equipment is connected to the lines of the communication system.
Another situation for which an isolation system is needed is that encountered in telephone party-line operation. An OFF-HOOK condition of the instrument belonging to one party interrupts service to all other parties. Only if the central office can disconnect any instrument found in an OFF-HOOK condition can the network be restored to operating condition.
Remote isolation devices currently available will respond to a signal voltage applied by automatic testing equipment (e.g., 180 volts DC) when the line under test is accessed. However, there are some serious problems with the devices currently in use. Many of the new switching systems use voltages for two party automatic number identification features, and other class mark testing that may cause trouble or provide the means to cause false operation of the remote isolation device. Generally, the known devices have their control circuits connected between one or both sides of the loop and ground and such systems are extremely susceptible to unwanted operation resulting from externally induced transients. The known systems tend to be complicated and costly to produce and not fully compatible with all existing communication networks.
It, therefore, is an object of the present invention to provide a remotely actuatable disconnect device for isolating the far end equipment from a communication loop, which device will not noticeably load the loop, will not disconnect telephone instruments in a normal ON-HOOK condition, is comparatively simple and inexpensive to produce, and avoids the disadvantages mentioned above.